I have to apologise for being unclear about what happened to the first batch of saturate. I thought I had said "Throw it out or use it for drain cleaner". As for rewriting, you shold have seen the first three versions.
I know that you are doing things with home made emulsions that require much more precise measurements than does film development, where much of the time we do not know for sure what contrast we need in the negative, and in roll film, we must often strike an average and do the rest in printing. The use of borax, metaborate, carbonate qnd many other chemicals can often be done as a chef does his favorite recipes..a dash of this and a pinch of that. To my knowledge, I have never in over 65 years used borax where a measurement error of 5 or 10 % would make a noticable difference. As for the guaranteed limits of chloride, sulphate and iron in technical grade powdered borax, a fingerprint on a mixing utensil might have as much effect. I know for a fact that I cannot see enough diference from adding 50 grams of sodium chloride to a liter of D-23 to make it worthwhile, so I cannot see how 700 ppm in 2 grams of borax would do any damage, nor 600 ppm of sulphate when 2 grams of Metol carries more than that into a liter of working D-76. Insoluble particles are specified <400 ppm in granular tech grade but none in powder tech grade. I suspect the insoluble particles are sand, but who knows? If so, it's not one of those things a production line would want to grind to powder.